docs: def from_clause(cls, clause):
          """ Factory method """
          field = clause[0]
          value1 = field_or_value(clause[1])
          op = None
          value2 = None
          if len(clause) > 2:
              op = clause[2]
              value2 = field_or_value(clause[3])
          return cls(field, value1, op, value2)